Micromorphological differences between some European and American <Emphasis Type="Italic">Fraxinus</Emphasis> (<Emphasis Type="Italic">Oleaceae</Emphasis>) species

Micromorphological differences in leaves and pollen between two American (Fraxinus americana L., F. pennsylvanica Marshall) and two European (F. angustifolia Vahl, F. excelsior L.) ash species were studied using scanning electron microscope. The types, dimensions and distribution of characteristic trichomes were established and measured. Capitate hairs on the leaves had the same shape in all researched ash species. Acicular hairs were regularly present in two American ash species, but very rarely in the glabrous phase of F. angustifolia and F. excelsior. Only F. americana had coronulate abaxial surface of leaves. Pollen of F. angustifolia and F. excelsior had 3 (tricolpate) apertures, and F. americana and F. pennsylvanica 4 (stephanocolpate) apertures. Based on the appearance of the reticulum it’s possible to clearly distinguish all four species. F. angustifolia and F. pennsylvanica had muri with transversal ridges and seldom granules. Muri of F. excelsior and F. americana had slightly visible transversal ridges, and because of that noticeable granules.     

Defining the twig fungal communities of Fraxinus species and Fraxinus excelsior genotypes with differences in susceptibility to ash dieback

Ash dieback disease (caused by Hymenoscyphus fraxineus) has affected European ash species (Fraxinus spp.) in recent decades. However, some Asian and American species of Fraxinus and certain genotypes of Fraxinus excelsior are less affected by the disease. We used ITS1-metabacoding to explore the drivers influencing diversity and composition of the twig fungal communities of Fraxinus species and F. excelsior genotypes. Our results revealed that fungi in the classes Eurotiomycetes and Dothideomycetes were among the most prevalent taxa in both Fraxinus species and F. excelsior genotypes. The diversity of the fungal communities differed significantly among Fraxinus species and could be explained by seed origin. Neither host genotype nor season had a significant effect on the community diversity of F. excelsior genotypes. On the other hand, the composition of twig fungal communities differed significantly among host species and among F. excelsior genotypes, and in F. excelsior there was also a significant effect of season on the composition of the fungal community. We did not find a clear effect of ash dieback susceptibility on either diversity or composition of fungal communities in twigs of Fraxinus species, although the effect was significant on the composition of fungal communities among F. excelsior genotypes. Our results demonstrated differences in fungal communities among species of Fraxinus and of F. excelsior genotypes, suggesting specific relationship between individual host genotypes and endophytic fungi.     

Visually Mediated ‘Paratrooper Copulations’ in the Mating Behavior of <Emphasis Type="Italic">Agrilus planipennis</Emphasis> (Coleoptera: Buprestidae), a Highly Destructive Invasive Pest of North American Ash Trees

The emerald ash borer, Agrilus planipennis, is a serious invasive pest of North American ash (Fraxinus) trees. In captivity, mating is initiated by beetles at least 10 days old, and appears to be based simply on random contact with a member of the opposite sex. In the field, male A. planipennis search the tree during flight, and attempt to copulate with dead beetles of both sexes pinned to leaves, after descending rapidly straight down onto the pinned beetles from a height of from 30 to 100 cm. All evidence suggests that males find potential mates using visual cues. Equal numbers of feral males approach all ‘dummy’ beetles; however, considerably more time is spent attempting copulation with dead females rather than males, suggesting a contact chemical cue. Sticky traps prepared from dead, pinned EAB capture crawling insects as well as male A. planipennis, at a rate similar to that at which small purple sticky traps of similar overall area capture crawling insects and both sexes of feral EAB.     

Genetic analysis of emerald ash borer (<Emphasis Type="Italic">Agrilus planipennis</Emphasis> Fairmaire) populations in Asia and North America

Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is an invasive pest of North American ash (Fraxinus spp.) trees first discovered outside of its native range of northeastern Asia in 2002. EAB spread from its initial zone of discovery in the Detroit, Michigan and Windsor, Ontario metropolitan areas, in large part, from inadvertent human-assisted movement of infested ash materials. EAB infestations are now known in 15 US states and two Canadian provinces. The primary goal of this study was to use molecular markers to characterize the population genetic structure of EAB in its native and introduced range. This information may provide valuable insights on the geographic origin, potential host range, invasion potential, and additional biological control agents for ongoing management efforts of this destructive wood-boring beetle. EAB were collected from 17 localities in its native Asian range and from 7 localities in North America, and population structure analyzed using mtDNA gene sequences, AFLP fingerprints, and alleles at 2 microsatellite loci. Analysis of mtDNA cytochrome oxidase subunit I gene (COI; 439 bp) sequences revealed all North American individuals carry a common mtDNA haplotype also found in China and South Korea. Additional mtDNA haplotypes observed in China and South Korea differed from the common haplotype by 1–2 nucleotide substitutions and a single individual from Japan differed by 21 nucleotide changes (4.8%). Analysis using AFLP fingerprints (108 loci) indicated Asian populations were more highly variable, yet had less overall population structure, than the North American populations. North American populations appear most closely related to populations in our sample from the Chinese provinces of Hebei and Tianjin City. Further, population assignment tests assigned 88% of the individual beetles from North America to either Hebei or Tianjin City.     

Rail transport as a vector of emerald ash borer

1. The emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive woodboring beetle native to northeastern Asia that continues to expand its range within North America and European Russia. The insect reproduces within and kills most North American species of ash Fraxinus spp.
2. Because both the adult and larval life stages of EAB are difficult to detect prior to development of tree symptoms, much work has focused on quantifying spread and clarifying the potential movement pathways to improve early detection and monitoring strategies.
3. In the present study, we retrospectively analyzed county‐level infestations of emerald ash borer in the state of Iowa, U.S.A., subsequent to the initial detection of EAB in 2010. Visual data analysis had suggested that new infestations were not in accordance with the expected patterns of establishment along roads, near campgrounds or by large population centres.
4. We found a positive correlation between the establishment and detection of EAB in Iowa counties and the length of railroads in each county. To our knowledge, this is the first statistically significant association between rail pathways and the spread of EAB on the North American continent.

     

Could phenotypic plasticity limit an invasive species? Incomplete reversibility of mid-winter deacclimation in emerald ash borer

The emerald ash borer (Agrilus planipennis, Coleoptera: Buprestidae) is a wood-boring invasive pest devastating North American ash (Fraxinus spp.). A. planipennis overwinters primarily as a freeze-avoiding prepupa within the outer xylem or inner bark of the host tree. The range of this species is expanding outward from its presumed introduction point in southwestern Michigan. We hypothesized that loss of cold tolerance in response to mid-winter warm spells could limit survival and northern distribution of A. planipennis. We determined whether winter-acclimatised A. planipennis prepupae reduced their cold tolerance in response to mid-winter warm periods, and whether this plasticity was reversible with subsequent cold exposure. Prepupae subjected to mid-winter warm spells of 10 and 15°C had increased supercooling points (SCPs) and thus reduced cold tolerance. This increase in SCP was accompanied by a rapid loss of haemolymph cryoprotectants and the loss of cold tolerance was not reversed when the prepupae were returned to −10°C. Exposure to temperatures fluctuating from 0 to 4°C did not reduce cold hardiness. Only extreme warming events for several days followed by extreme cold snaps may have lethal effects on overwintering A. planipennis populations. Thus, distribution in North America is likely to be limited by the presence of host trees rather than climatic factors, but we conclude that range extensions of invasive species could be halted if local climatic extremes induce unidirectional plastic responses.     

Effects of grafting on host plant resistance in ash (Fraxinus spp.) to emerald ash borer (Agrilus planipennis Fairmaire)

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Anthocyanin biosynthesis genes location and expression in wheat–rye hybrids

Studies into gene expression in a foreign background contribute toward understanding of how genes derived from different species or genera manages to co-exist in a common nucleus, on the one hand, and help to estimate possible effectiveness of wide hybridization for cultivated plant improvement, on the other hand. The aim of this study was to investigate conservation of wheat and rye expression networks, using the anthocyanin biosynthesis pathway (ABP) genes as a model system. We isolated and analyzed ABP genes encoding enzymes acting at different steps of the pathway: chalcone-flavanone isomerase (CHI), flavanone 3-hydroxylase (F3H), anthocyanidin synthase (ANS), and anthocyanidin-3-glucoside rhamnosyltransferase (3RT). The rye ABP genes locations we determined (Chi on chromosome 5RL, F3h on 2RL, Ans on 6RL, 3Rt on 5RL, the regulatory Rc—red coleoptile—gene on 4RL) were in agreement with the rearrangements established between rye and wheat chromosomes. Expression of the ABP structural genes was studied in wheat–rye chromosome addition and substitution lines. F3h activation by the Rc gene was found to be critical for the red coleoptile trait formation. It was shown that the rye regulatory Rc gene can activate the wheat target gene F3h and vice versa wheat Rc induces expression of rye F3h. However, lower level of expression of rye F3h in comparison with that of the two wheat orthologues in the wheat–rye chromosome substitution line 2R(2D) was observed. Thus, although work of the wheat and rye ABP gene systems following the formation of wheat–rye hybrids is finely coordinated, some divergence exists between rye and wheat ABP genes, affecting level of gene expression.     

North American arthropods at risk due to widespread Fraxinus mortality caused by the Alien Emerald ash borer

Emerald ash borer (Agrilus planipennis Fairmaire) (EAB), an alien invasive wood-boring buprestid beetle, is causing large-scale decline and mortality of the most widely distributed species of ash (Fraxinus spp.) trees endemic to eastern North America. We determined which arthropod species that are associated with ash may become threatened, endangered, and co-extinct with the demise of ash as a dominant tree species. A literature survey revealed that 43 native arthropod species in six taxonomic groups (Arachnida: Acari; Hexapoda: Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera) are known to be associated only with ash trees for either feeding or breeding purposes, and thus face high risk of endangerment. Most of these species are gall-formers followed by folivores, subcortical phloem/xylem feeders, sap feeders, and seed predators. Another 30 arthropod species are associated with 1–2 host plants in addition to ash, and herbivory on these hosts may increase as these arthropods shift from declining ash trees. Extirpation of arthropods dependent upon ash may unleash multiple extinctions of affiliated species with which they may be inextricably linked. The demise of North American ash species due to EAB is expected to lead to biotic loss with cascading ecological impacts and altered processes within forested ecosystems.     

Transport of Photoassimilates in Young Trees of Fraxinus and Sorbus: Measurement of Translocation in vivo

Abstract: Translocation of photoassimilates was studied on 2-year-old trees of Fraxinus excelsior and Sorbus aucuparia using the short-lived isotope ¹¹C. Leaflets of different leaves on the same plants were radiolabeled showing that both carbon distribution and speeds of transport may vary with leaf position. Within 2 h after pulse feeding with ¹¹CO₂, mainly the lower leaves distributed radiolabel to the roots in Fraxinus, whereas in Sorbus, the upper leaves were also involved. By repeated pulse applications to selected leaves, temporal profiles of ¹¹C transport were followed on individual plants from April to October. Early in the season, within 2 h after pulse labelling, 30–40% of the fixed radiolabel was exported from leaves in Fraxinus and about 20% in Sorbus. Thereafter export started to decline, particularly in Fraxinus, and the distribution of radiolabel between stem and roots could alter depending on the position of the feed leaf. Speeds of translocation obtained along the rachis and stem showed high variability, but they did not necessarily slow down before the end of the season. The speeds monitored at the rachis of Fraxinus leaves (30–75 cm h^?1) were generally lower than those found on Sorbus (50–130 cm h^?1). As reported in the literature, the two tree species translocate different carbohydrates and show remarkable differences in the ultrastructure of their vascular systems. In that context it is interesting that the temporal profiles of ¹¹C radioactivity obtained from F. excelsior and S. aucuparia could clearly be distinguished by their characteristic shapes. The results are discussed in terms of anatomical characteristics of the conducting tissues and possible differences in phloem loading.     

Effects of the emerald ash borer invasion on the community composition of arthropods associated with ash tree boles in Maryland,U.S.A.

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Phytoextraction capacity of trees growing on a metal contaminated soil

Phytoremediation is an innovative biological technique to reclaim land contaminated by heavy metals or organic pollutants. In the present work, we studied the ability of five woody species to extract heavy metal (copper, zinc or cadmium) from a polluted soil to their above-ground tissues. Metal content in leaves and twigs was determined. Salix and Betula transferred zinc and cadmium to leaves and twigs, but Alnus, Fraxinus and Sorbus excluded them from their above-ground tissues. None of the species considered transferred copper to the shoots.     

Validation and application of reference genes for quantitative gene expression analyses in various tissues of <Emphasis Type="Italic">Bupleurum chinense</Emphasis>

It is crucial to select stable references in gene expression analyses using quantitative real-time PCR (qRT-PCR). In this work, seven frequently used reference genes, 18S, Actin, EF1α, α-tubulin, β-tubulin, Cyclophilin and Cytoplasmic ribosomal protein L2 (L2), from Bupleurum chinense DC. were evaluated as the internal control in five tissues, roots, stems, leaves, flowers and fruits, before tissue specific gene expression assays. The results showed that β-tubulin was the most stable and reliable reference gene among the seven candidate genes in the measured tissues. The expression levels of four genes involved in saikosaponins (the pharmacological active compounds of B. chinense) biosynthesis, HMGR, IPPI, FPS and β-AS, were assayed with β-tubulin as the internal control in the five tissues. All the four genes were expressed in the five tissues with different profiles and HMGR in the order of roots > flowers, stems and leaves > fruits, IPPI of stems > leaves and fruits > roots and flowers, FPS of flowers > fruits > stems and roots > leaves and β-AS of roots > flowers, stems and fruits > leaves. The genes of FPS and β-AS were expressed predominantly in flowers and roots, respectively. This study may provide a suitable internal control for quantitative gene expression assays in various tissues and give insight into the tissue expression profiles of four saikosaponins biosynthesis-involved genes of medicinal B. chinense.     

Advances toward DNA-based identification and phylogeny of North American Armillaria species using elongation factor-1 alpha gene

The translation elongation factor-1 alpha (EF-1α) gene was used to examine the phylogenetic relationships among 30 previously characterized isolates representing ten North American Armillaria species: A. solidipes (=A. ostoyae), A. gemina, A. calvescens, A. sinapina, A. mellea, A. gallica, A. nabsnona, North American biological species X, A. cepistipes, and A. tabescens. The phylogenetic relationships revealed clear separation of all ten North American Armillaria species, with the exception of one A. gallica isolate that perhaps represents an unnamed cryptic species. These results indicate that the EF-1α gene could potentially serve as a diagnostic tool for distinguishing among currently recognized North American biological species of Armillaria.     

Interspecific proteomic comparisons reveal ash phloem genes potentially involved in constitutive resistance to the emerald ash borer

The emerald ash borer (Agrilus planipennis) is an invasive wood-boring beetle that has killed millions of ash trees since its accidental introduction to North America. All North American ash species (Fraxinus spp.) that emerald ash borer has encountered so far are susceptible, while an Asian species, Manchurian ash (F. mandshurica), which shares an evolutionary history with emerald ash borer, is resistant. Phylogenetic evidence places North American black ash (F. nigra) and Manchurian ash in the same clade and section, yet black ash is highly susceptible to the emerald ash borer. This contrast provides an opportunity to compare the genetic traits of the two species and identify those with a potential role in defense/resistance. We used Difference Gel Electrophoresis (DIGE) to compare the phloem proteomes of resistant Manchurian to susceptible black, green, and white ash. Differentially expressed proteins associated with the resistant Manchurian ash when compared to the susceptible ash species were identified using nano-LC-MS/MS and putative identities assigned. Proteomic differences were strongly associated with the phylogenetic relationships among the four species. Proteins identified in Manchurian ash potentially associated with its resistance to emerald ash borer include a PR-10 protein, an aspartic protease, a phenylcoumaran benzylic ether reductase (PCBER), and a thylakoid-bound ascorbate peroxidase. Discovery of resistance-related proteins in Asian species will inform approaches in which resistance genes can be introgressed into North American ash species. The generation of resistant North American ash genotypes can be used in forest ecosystem restoration and urban plantings following the wake of the emerald ash borer invasion.     

Decreased emergence of emerald ash borer from ash treated with methyl jasmonate is associated with induction of general defense traits and the toxic phenolic compound verbascoside

The emerald ash borer (EAB; Agrilus planipennis Fairmaire) is causing widespread mortality of ash (Fraxinus spp.) in North America. To date, no mechanisms of host resistance have been identified against this pest. Methyl jasmonate was applied to susceptible North American and resistant Asian ash species to determine if it can elicit induced responses in bark that enhance resistance to EAB. In particular, phenolic compounds, lignin, and defense-related proteins were quantified, and compounds associated with resistance were subsequently tested directly against EAB larvae in bioassays with artificial diet. MeJA application decreased adult emergence in susceptible ash species, comparable to levels achieved by insecticide application. Concentration of the phenolic compound verbascoside sharply increased after MeJA application to green and white ash. When incorporated in an artificial diet, verbascoside decreased survival and growth of EAB neonates in a dose-dependent fashion. Lignin and trypsin inhibitors were also induced by MeJA, and analogs of both compounds reduced growth of EAB larvae in artificial diets. We conclude that the application of MeJA prior to EAB attack has the ability to enhance resistance of susceptible ash trees by inducing endogenous plant defenses, and report evidence that induction of verbascoside is a mechanism of resistance to EAB.